Top scientists are warning that we all need to eat less meat and dairy products.
But it's not for our health - it's to help the environment.
Forests are being cut down to make space for farm animals and for fields to grow their food.
This deforestation raises levels of carbon in the atmosphere, but also, burps from the animals add methane gas too.
These gases are speeding up the rate the planet's climate is changing, says the report in the Nature Climate Change journal.